Filter press, more particularly for dewatering sludge in sewage treatment plants

ABSTRACT

A process for dewatering sludge particularly for dewatering sludge in sewage treatment plant by means of a filter presshaving belts one at least of which is a filter belt, the sludge being conveyed around a drum between belts both of which pass around the drum the sludge being squeezed between the belts as it is conveyed around the drum by the belts.

United States Patent [1 1 B'ahr FILTER PRESS, MORE PARTICULARLY FORDEWATERING SLUDGE IN SEWAGE TREATMENT PLANTS [76] Inventor: AlbertBiihr, Parallelstrasse 2a,

Elversberg/Saar, Germany [22] Filed: June 7, 1971 [21] Appl. N0.:150,356

[52] US. Cl. 210/386, 210/401 [51] Int. Cl BOId 33/04 [58] Field ofSearch 210/77, 386 401 [56] References Cited UNITED STATES PATENTS8/1969- Pastoors et a1. 210/386 X 10/1971 Adamski et a1 210/386 XFOREIGN PATENTS OR APPLICATIONS France 210/401 [451 July 3,1973

732,987 2/1943 Germany 210/77 1,199,656 12/1959 France 210/77 305,37911/1915 Germany 210/77 Primary ExaminerJohn Adee Attorney-Robert H.Jacob 5 7 1 ABSTRACT A process for dewatering sludge particularly fordewatering sludge in sewage treatment plant by means of a filterpresshaving belts one at least of which is a filter belt, the sludgebeing conveyed around a drum between belts both of which pass around thedrum the sludge being squeezed between the belts as it is conveyedaround the drum by the belts.

6 Claims, 9 Drawing Figures PATENTEDJUL 3:915

- 3.743.100 sum 1 or 1 FIG.1

IN V EN TOR PATENTEUJUL 3197s 3.743.100

INVEN TOR 4151997 5/1 /7 PATENIEDJUL 3 I915 SHEET 3 0F 7 INVENTOR 654??"6 9W BY r INVEN TOR FILTER PRESS, MORE PARTICULARLY FOR DEWATERINGSLUDGE IN SEWAGE TREATMENT PLANTS The present invention relates to afilter press, for use for example for dewatering sludge in sewagetreatment plants.

It is known for the sludge which accumulates in sewage treatment plantsto be dewatered, after an addition of organic or inorganic filteradjuvants, in a filter-belt press comprising a horizontal filter beltand a pressure belt thereabove. Not only is the construction of suchpresses relatively difficult and complex but they have more particularlythe disadvantage of requiring special precautions to prevent the beltsfrom wandering. Also,

filtration performance is often unsatisfactory.

Also known are tower presses wherein two filter belts move atright-angles to one another under pressure; in contrast to filter-beltpresses, both the belts of tower presses are used for filtering, butconstruction is very costly and the system has the disadvantage of thefiltrate being continuously removed through the whole construction;also, not only is filtration sometimes unsatisfactory but thereareparticular difficulties in lateral sealing of the two filter belts.

It is an object of the invention to obviate these disadvantages and toprovide a filter press, more particularly for dewatering sludge insewage tratment plant, the

press providing satisfactory filtration while being of fairly simpleconstruction and taking up little space and ensuring a low residualwater content.

Accordingly, the invention comprises a filter press having belts one atleast of which is a filter belt extending around a drum and the sludgefor dewatering is introducible between such belts. The press cancomprise two belts both of which are filter belts. According to afeature of the invention, an inner filter belt extends in a closed looparound the drum and a second belt extends around the drum in a doubleloop the opposite closed ends of which are spaced apart.

It is known for two filter belts to extend around a drum in vacuum drumfilters. However, in the known filters both the filter belts extendaround the drum in a concentrically closed path and the filter cake isfed on the outside of the outer belt. A feature of the invention,however, is that dewatering is performed between two filter belts whichextend around a drum.

Advantageously, the outer belt engages around the inner belt withpressure, so that the filter cake can be subjected to the necessarypressure. The pressure can be produced either just by the tension of theouter belt or by special load applying means e.g. pressure rollers.

According to a feature of the invention, the drum is of openconstruction. For example the same can incorporate rollers, in whichcase over at least some of their path around the drum the two belts areguided between radially inner rollers and radially outer rollers, if asabove mentioned, the load applying means are pressure rollers.Preferably, the roller pressure is adjustable so that it can increasealong the pressing path according to the nature of the sludge and to therequired residual water content. Advantageously in this case, the innerrollers and the outer rollers are in staggered relationship to oneanother, to achieve squeezing of the filter cake between the two ringsof rollers, the filter cake being alternately compressed and released.

The invention also relates to a process for dewatering sludge, moreparticularly clarifying sludge of sewage treatment plants; according toa main feature of the process, the sludge is dewatered between two beltswhich extend around a drum, with pressure. Preferably, the sludge issqueezed between the belts. Very advantageously in this case, drum speedleads or lags on the speed of the belts, so that the different speedshelp to break up the cohesion of the filter cake between the variousinner rollers and outer rollers, thus greatly improving dewatering.

An embodiment of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 is a flow diagram for sludge dewatering according to theinvention;

FIG. 2 is a side view of a drum filter press according to the invention;

FIG. 3 is a view of the drum filter press in crosssection;

FIG. 4 is a view of the drum filter press in longitudinal section;

FIG. 5 is a plan view of the drum filter press;

FIG. 6 is an end view of the feed side and ejection side, and

FIGS. 7-9 are fragmentary views showing details of the construction.

Referring to FIG. 1 of the drawings, the installation shown has a sludgetank I, and an additives tank II for water and coagulant; water mixedwith coagulant or some other filter adjuvant is supplied to coagulanttank Ill. There is a sludge dispenser IV and a coagulant dispenser V;coagulant is added to the sludge in a mixing tank VI and the resultingmixture is supplied to a drum filter press VII constructed in accordancewith the invention.

Referring to FIGS. 2 to 6 of the drawings, an endless filter belt 1extends around a cage structure or drum 2 and is driven by a drivingdrum 3, the belt 1 extending around the cage structure or drum 2 in aclosed loop. A second endless filter belt 4 extends around drum 2radially outwards of belt 1. The filter belt 4 is a double loop the endsof which are spaced apart from one another at one side of the drum, oneend passing around a driving drum driven by a driving motor 5, the otherend passing around a reversing drum 6.

In the embodiment shown, the filter press comprises a machine frame 14supporting the drum 2 which is of open construction and comprises twocircular end frames 7 on a shaft 9 supported at its opposite ends in themachine frame 14. The end frames 7 are spaced apart lengthwise of theshaft 9 and support between them a plurality of rollers 8 spacedcircumferentially from one another around the end frames the rollersextending parallel to the shaft 9 the endless belt 1 bearing on therollers 8. The drum 2 is positively driven by a variable speed drivingmotor 11 mounted on the machine frame 14 through gears 10. Alternativeto the positive drive, the drum can be capable of free rotation so as tobe rotatable by the endless belts.

Disposed radially outwards of the rollers 8 of drum 2, are a pluralityof counter rollers 12, referred to as pressing rollers. The rollers 12are supported by the machine frame 14 and only partially around the drum2, the rollers 12 being circumferentially spaced from one another. Therollers 12 are'disposed radially outwards of the endless filter belt 4.The rollers 12 are mounted so as to be capable of radial movement andare spring loaded by springs 13 the spring action urging the rollersradially inwards to apply pressure to the filter belts. Means areprovided to permit variation of the spring loading so that the pressureapplied by the roll ers 12 can be varied. Further the pressure can beadjusted so that the same is different at predetermined circumferentialportions. For example it may be convenient for the compression springs13 to be so adjusted that the spring pressure increases along thepressing path, to give a setting at which the rollers 12, which are allstaggered in relation to the inner rollers 8, are pressed between therollers 8 by spring pressure at the end of the pressing path so that thetwo filter belts follow a sinuous path between the various rollers asshown in FIG. 7.

The driving motor 3 for filter belt 1 is bodily movable against springloading provided by compression spring 15 the loading of which isadjustable. Similarly, the driving motor for the filter belt 4 is bodilymovable against spring loading provided by compression spring 16 theloading of which is adjustable. Such arrangements maintain the tensionof the filter belts during operation of the press and also permit thetension to be adjusted.

Sludge is supplied to the filter belt 4 through feed pipe 17 and nozzle18 the sludge being delivered onto a central portion of the filter beltand in a quantity such as exactly to fill up the space between the twofilter belts over the pressing path, thus obviating the necessity forspecial lateral sealing means to prevent overflow at the edges of thefilter belts. It may however be desirable for one or both of the filterbelts to have thickened side edges to provide lateral sealing ashereinafter described. The sludge supplied through the pipe 17 andnozzle 18 is squeezed and conveyed between the two belts l and 4 as ifin a chamber, the two filter belts running at the same speed, which maybe varied.

. The expressed water issues inwardly and outwardly through the belts 1,4, is collected in receptacles 19, 20 and supplied via sump 21 tocollecting pipe 22. For improved dewatering, the rollers 8, 12, are,conveniently, formed with grooves 23.

The expressed filter cake is ejected near the driving roller 3 at aplace 24; if required, scrapers 25 or appropriately disposed blowingnozzles can be provided to detach the filter cake. The filter belts arecleaned by sprinklers 26.

As shown diagrammatically in FIG. 7, the pressing rollers 12 can, moreparticularly over about the last third of the pressing path around thedrum, be pressed so tightly into the gaps between the rollers 8 byincreasing the stressing of the springs 13 that the belts 1, 4 and thefilter cake move sinuously and the cake is given alternate squeezing andrelease. To increase this effect the drum 2 can be driven faster orslower than the filter belts. As FIG. 8 shows, the rollers 8, 12 can betaper rollers.

As already mentioned, the quantity of filter cake supplied can be suchthat no lateral sealing is necessary between the filter belts l and 4.However, and as shown in FIG. 9, the filter belts l, 4 can have lateraledge thickenings 28 to act as a lateral seal.

The invention therefore provides a filter press which is of simple androbust construction, takes up little space and provides a high andadjustable filtering capacity. There is no risk of the two filter beltsof the press according to the invention wandering. A particularadvantage provided by the invention is inter alia adjustability ofpressing capacity, a low residual water content being achieved for areduced power consumption. The filter press according to the inventionis intended more particularly for the dewatering of communal sludge, butit can be used for any other sludges such as e.g. industrial effluent,hydroxide sludge, preparation sludge, wet dust removal sludge or thelike.

I claim:

1. A filter press comprising a machine frame, a cylindrical cagestructure mounted on said frame for rotation about an axis and having acircular series of relatively rotatable belt supporting rollers on apitch circle concentric with the axis of said cage structure; a circularseries of counter rollers concentric with the axis of said cagestructure; bearing means on said machine frame mounting said counterrollers on a pitch circle of larger diameter than said pitch circle ofsaid belt supporting rollers and supporting said counter rollers onparallel axes extending axially of said cage sturcture; first and secondendless belts extending partially around said cage structure betweensaid belt supporting rollers and said counter rollers, at least one ofsaid belts being a filter belt, and the belt supported by said cagestructure presenting its radially outer side to the radially inner sideof the other belt; roller means cooperable with said other belt forplacing the latter in double loop formation and presenting the closedends of the double loop in relatively spaced relation at one side ofsaid cage structure; and sludge feeding means operable to deliver sludgebetween the belts at said one side of said cage structure.

2. A filter press as set forth in claim 1 wherein said bearing means forsaid counter rollers support the latter for radial movement relative tosaid cage structure, and wherein resilient means are operativelyinterposed between said machine frame and said bearing means so as toyieldingly urge said counter rollers toward said cage structure.

3. A filter press as set forth in claim 1 wherein the number of beltsupporting rollers on said cage structure is larger than the number ofcounter rollers on said machine frame.

4. A filter press as set forth in claim 1 and further comprisingvariable speed power transmitting means for driving said cage structure.

5. A filter press as set forth in claim I wherein both of said belts arefilter belts and wherein fluid intercepting means are mounted withinsaid cage structure.

6. A filter press as set forth in claim 1, where said axis is disposedhorizontally.

a: m a e a

1. A filter press comprising a machine frame, a cylindrical cagestructure mounted on said frame for rotation about an axis and having acircular series of relatively rotatable belt supporting rollers on apitch circle concentric with the axis of said cage structure; a circularseries of counter rollers concentric with the axis of said cagestructure; bearing means on said machine frame mounting said counterrollers on a pitch circle of larger diameter than said pitch cIrcle ofsaid belt supporting rollers and supporting said counter rollers onparallel axes extending axially of said cage structure; first and secondendless belts extending partially around said cage structure betweensaid belt supporting rollers and said counter rollers, at least one ofsaid belts being a filter belt, and the belt supported by said cagestructure presenting its radially outer side to the radially inner sideof the other belt; roller means cooperable with said other belt forplacing the latter in double loop formation and presenting the closedends of the double loop in relatively spaced relation at one side ofsaid cage structure; and sludge feeding means operable to deliver sludgebetween the belts at said one side of said cage structure.
 2. A filterpress as set forth in claim 1 wherein said bearing means for saidcounter rollers support the latter for radial movement relative to saidcage structure, and wherein resilient means are operatively interposedbetween said machine frame and said bearing means so as to yieldinglyurge said counter rollers toward said cage structure.
 3. A filter pressas set forth in claim 1 wherein the number of belt supporting rollers onsaid cage structure is larger than the number of counter rollers on saidmachine frame.
 4. A filter press as set forth in claim 1 and furthercomprising variable speed power transmitting means for driving said cagestructure.
 5. A filter press as set forth in claim 1 wherein both ofsaid belts are filter belts and wherein fluid intercepting means aremounted within said cage structure.
 6. A filter press as set forth inclaim 1, where said axis is disposed horizontally.